8/2/2019 Fuses for 214 AC and DC-CPU Power Supply, The Inputs and the Outputs Www.otomasyonegitimi.com

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QUESTION:Which Fuses are recommended for protection of the 214 AC and DC-CPUs power supply, the inputsand the outputs?

ANSWER:In the following section you get a list of the types, release behaviour and rated current for the fuses,which are recommended to protect the S7-200 CPU 214 AC/DC power supply, inputs and outputs:

1. AC Power Supply :External fuse sized to protect external wiring. Any failure within the CPU power supply willresult in internal fuse opening. The only requirement is that the external fuse carry the initialstart up surge, which will be less than 20A peak at 264VAC and with a half-width of less than10 ms, and the rated steady state input current.

2. DC Power Supply :External fuse sized to protect external wiring and source of DC power. Any failure within theCPU power supply will result in internal fuse opening. The only requirement is that the externalfuse carry the initial start up surge, which will be less than 10A peak and with a half-width of

less than 5 ms, and the rated steady state input current.3. DC inputs :

External fuse sized to protect external wiring.4. Relay outputs :

Fusing to protect external wiring only is acceptable. Protection of relay closing on a short circuitis very difficult, the resulting arc as the relay closes is very harmful to the contacts. To protectclosed contacts from a short circuit, a 2.5A fuse with an I*I*T rating of 25 will protect thecontacts and should allow typical load surges. ( IEC 127-3/IV, the fuse will carry 5A for 1second, 7A for 0.5 seconds, 15A for 100 ms). If individual fusing of each output is not desired,a 10A fuse with I*I*T rating of 100 on each common is recommended.

5. DC outputs :Fusing to protect external wiring and DC power source only is acceptable. Transistor outputswill typically not be protected by a fuse unless additional current limiting is included. Thetransistor bond wires will open faster than a commercial fuse. If short circuits are expected, a 3

ohm resistor in series with each output, or a DC power source that instantly limits maximumcurrent to 8A, will allow an external fuse time to act. External fuse for this case should be 1A orless with an I*I*T rating of 5.5 or less.

Entry ID:831492 Date:1999-04-21

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